Prop question.
For most motors you can look online to see what the proper size and pitch prop your motor and esc can handle. Those diagrams usually list amps so that is how you can determine if your esc can handle the prop. Another way is to just fly it and if the motor or esc is too hot to touch the prop is either too large or the pitch on it is too steep.
Prop nut question.
I have had no problems with using the stock prop nut in both counter clockwise and clockwise directions. The only time it came off is when I crashed the plane. You can also go to the hardware store with the motor and get some lock nuts if you want to make certain it does not fall off.
Landing gear question.
I would try and find some thick wire (I am unsure of the correct thickness unfortunately) to use for landing gear instead of the 3d printed ones. However I bet that there are some really good 3d printed options for landing gear I just don't know of any off hand.
Camera question.
If you don't want to see the prop then a pusher is the right way to go, and for your tractor airplanes I would recommend just pointing it at cool angles to try and get some interesting shots. I personally like pointing mine at the tail from the fuselage or the wing tip. I will warn however if you try the wingtip option make sure that you put something of equal weight on the other wing about the same distance out from the fuselage as the camera is.
I hope this helped! thanks for that I recently got into the hobby and i’m just wondering can you use a 1400kv motor for the mighty mini sportster??